1. Field of the Invention
This invention relates to a platen for use in a recording device, and also to a method for manufacturing the same.
2. Description of Prior Art
A non-impact type recording system, such as, for example, a heat-transfer type recording device, performs its recording in a dot-pattern by: (1) repeated operations of press-contacting a heat-generating section provided on a recording head to a recording sheet laid on a platen; (2) moving the recording head in its printing direction, while driving the heat generating section, thereby performing the recording of one line; and (3) forwarding the recording sheet by one increment in the line direction.
Therefore, in order to carry out adequate recording by this system, it is necessary that the heat generating section of the recording head be in perfect surface-contact with the recording sheet, incremental feed maintaining the appropriate pressure therewith. Further, the must always be constant.
For satisfying such conditions, there has so far been used widely, in this type of the recording device, a platen of a construction as shown in FIG. 1 of the accompanying drawing.
In the drawing, the platen 1 has a rectangular planar shape and is made of a material such as, for instance, rubber having a rubber hardness of 50.degree. or so. The platen is fixed on a frame 2 (a supporting member) by various methods such as gluing, two-sided adhesive tape, and others. The surface of the platen 1, at its side facing the recording head 5, is covered with a Teflon sheet 3 having a small frictional coefficient. The Teflon sheet 3 is fixed at its upper end (part 3a) and lower end (part 3b) onto the surfaces of the frame 2, on the upper and lower sides of the platen 1, with two-sided adhesive tape.
When recording, the recording sheet 4 is press-contacted to the Teflon sheet 3 fixed on the surface of the platen 1, and the recording operation is effected in accordance with the above-mentioned procedures.
According to the above-described construction, since the platen 1 is formed of rubber having elasticity, the entire surface of the heat generating section in the recording head 5 can be brought into good contact with the recording sheet 4 at the time of the recording. Moreover, since the Teflon sheet produces low friction sliding against the recording head 5, the recording head 5 can be prevented.
In addition, the small frictional coefficient of the Teflon sheet 3 provides better sliding of the recording sheet 4 on and along the platen 1, when forwarding the recording sheet in the line direction, preventing disturbance in the forwarding pitch in the line direction.
Further, the part of the Teflon sheet 3 extending at an incline below the platen 1 serves to guide the recording sheet 4, providing smooth insertion of the recording sheet 4, between the platen 1 and the recording head 5 to its designated position.
In the above-described construction, however, the manual fastening of the teflon sheet 3 onto the surface of the platen 1, at the time of assembly, without incurring creases and slack in the sheet, requires a high degree of technique. Therefore, these creases and slack tend to occur readily at the time of assembly. Further, because the adhesive strength between the Teflon sheet 3 and the platen 1 is weak, there is a high possibility of such creases and slack occurring when the Teflon sheet 3 is squeezed by the recording head 5.
When the creases and slack are created in the Teflon sheet 3, the heat generating section of the recording head 5 and the recording sheet 4 at this portion of the Teflon sheet 3 make poor contact between then with the consequence that the recorded portion becomes blurred, and it is difficult to obtain a favorable recording. Further, at the creased or slackened portion, the Teflon sheet 3 tends to break or wear-out. Such breakage at one small portion spreads over the surrounding area in a short period of time, so that the Teflon sheet 3 becomes useless within a short time.
Moreover, manual fixing the Teflon sheet 3 as mentioned above is not suitable for industrialized mass-production, and disadvantaeously pushes up the manufacturing cost.
With a view to elminating the above-described disadvantages inherent in the conventional platen for the recording apparatus, various proposals have been made for a platen material having: appropriate elasticity, small frictional coefficient on its surface, and high mechanical strength at the surface layer constituting the surface of the platen.
Examples of the proposed platen materials are as follows: one composed of a rubber sheet with its surface having been chemically treated and a Teflon sheet adhere to the surface of the thus treated rubber sheet, thereby increasing the adhesive strength between the Teflon sheet and the rubber sheet; one composed of a Teflon sheet and a rubber sheet, both being simultaneously molded to increase the degree of contact of the Teflon sheet to the rubber sheet; one composed of a rubber sheet alone with its surface having been subject to a fluorine-substituting treatment, thereby reducing the frictional coefficient of its surface to that of Teflon; or others.
According to the method for manufacturing the platen using these materials, a rectangular planar rubber sheet 6 as shown in FIG. 2A is first formed of a rubber material. Then, one surface of the rubber sheet 6 is joined with the Teflon sheet in a manner to obtain high mechanical strength as mentioned above. Alternatively, it is subjected to the fluorine-substituting treatment, thereby forming a surface layer 7 with a small frictional coefficient on the surface of the rubber sheet. Thereafter, as shown in FIG. 2C, the treated rubber sheet 6 is served along solid lines A at equally spaced intervals corresponding to the height of the resulting platen to thereby obtain individual platens 8. The solid lines A are parallel to one another and extend in the direction perpendicular to the longitudinal direction of the rubber sheet.
In view, however, of the fact that the thus manufactured platen 8 is rectangular in its cross-section, when it is fixed onto the frame 2 in such a manner that its surface layer 7 is projected from the front face of the frame 2 with a predetermined height as shown in FIG. 3, the lower and surface 8a of the platen 8 projects perpendicularly from the front surface of the frame 2 for the above-mentioned predetermined height.
As a result, when the recording sheet 4 is being inserted between the recording head 5 and the platen 8, the leading edge of the recording sheet 4 occasionally collides with the lower end face 8a of the platen 8, and is folded or otherwise crimped, preventing insertion between the recording head and the platen.